Registration of 6-DOFs electrogoniometry and CT medical imaging for 3D joint modeling

Abstract

The paper describes a method in which two data-collecting systems, medical imaging and electrogoniometry, are combined to allow the accurate and simultaneous modeling of both the spatial kinematics and the morphological surface of a particular joint. The joint of interest (JOI) is attached to a Plexiglas jig that includes four metallic markers defining a local reference system (R GONIO) for the kinematics data. Volumetric data of the JOI and the R GONIO markers are collected from medical imaging. The spatial location and orientation of the markers in the global reference system (R CT) of the medical-imaging environment are obtained by applying object-recognition and classification methods on the image dataset. Segmentation and 3D isosurfacing of the JOI are performed to produce a 3D model including two anatomical objects—the proximal and distal JOI segments. After imaging, one end of a custom-made 3D electrogoniometer is attached to the distal segment of the JOI, and the other end is placed at the R GONIO origin; the JOI is displaced and the spatial kinematics data is recorded by the goniometer. After recording, data registration from R GONIO to R CT occurred prior to simulation. Data analysis was performed using both joint coordinate system (JCS) and instantaneous helical axis (IHA). Finally, the 3D joint model is simulated in real time using the experimental kinematics data. The system is integrated into a computer graphics interface, allowing free manipulation of the 3D scene. The overall accuracy of the method has been validated with two other kinematics data collection methods including a 3D digitizer and interpolation of the kinematics data from discrete positions obtained from medical imaging. Validation has been performed on both superior and inferior radio-ulna joints (i.e. prono-supination motion). Maximal RMS error was 1° and 1.2 mm on the helical axis rotation and translation, respectively. Prono-supination of the forearm showed a total rotation of 132° for 0.8 mm of translation. The method reproducibility using JCS parameters was in average 1° (maximal deviation=2°) for rotation, and 1 mm (maximal deviation=2 mm) for translation. In vitro experiments have been performed on both knee joint and ankle joint. Averaged JCS parameters for the knee were 109°, 17° and 4° for flexion, internal rotation and abduction, respectively. Averaged maximal translation values for the knee were 12, 3 and 4 mm posteriorly, medially and proximally, respectively. Averaged JCS parameters for the ankle were 43°, 9° and 3° for plantarflexion, adduction and internal rotation, respectively. Averaged maximal translation values for the ankle were 4, 2 and 1 mm anteriorly, medially and proximally, respectively.